The background art teaches a variety of polymeric absorbent materials. U.S. Pat. No. 4,090,013 issued to Ganslaw et al. on May 16, 1978 teaches a water absorbent polymer for use in absorbent diapers or dressings. The absorbent in Ganslaw is a three component polymer having a long chain neutralized polyacrylic acid polyelectrolyte; chain extenders of di-functional monomers such as allyl methacrylate; and trivalent metal cations complexing and cross-linking the long chain polyelectrolytes.
Compositions using zinc are taught in the Background Art: U.S. Pat. No. 3,959,237 issued to Blank on May 25, 1976; U.S. Pat. No. 4,066,584 issued to Allen on Jan. 3, 1978; and U.S. Pat. No. 3,404,134 issued to Rees on Oct. 1, 1968.
British Pat. No. 869,333, published on May 31, 1961 of Rohm & Haas Company discloses acrylic polymers cross-linked with divalent calcium ions added as calcium acetate and alkali metal salt of methacrylic or acrylic acid.
Use of vinyl cross-linking agents is taught in U.S. Pat. No. 3,157,623 issued to Braun on Nov. 17, 1964. Use of triethylene glycol dimethacrylate as a cross-linking compound to increase gel viscosity in ethyl acrylate polymers is taught in the article by Stephen L. Rosen, "Some Rheological Properties of a Linear-Gel Polymer System", No. 7, APPLIED POLYMER SYMPOSIA, 127-141 (1968).
Absorbent articles containing an absorbent polymer are taught in U.S. Pat. No. 3,686,024 issued to Nankee et al. on Aug. 22, 1972 and U.S. Pat. No. 3,366,582 issued to Adams et al. on Jan. 30, 1968.
Grafting of acrylic acid to cellulose is taught in U.S. Pat. No. 3,457,198, issued to Sobolov on July 22, 1969.